JP2012-255642A and JP4557874B disclose a magneto-caloric effect type heat pump apparatus which is one embodiment of the thermo-magnetic cycle apparatus which uses a temperature characteristic of a magnetic substance. The documents propose heat pump apparatuses using the magneto-caloric effect of the magneto-caloric element which is a magnetic substance. The proposed apparatuses have a magnetic field modulating device having a permanent magnet and yoke members forming a magnetic path. The magnetic field modulating device cyclically and alternately switches a state of external magnetic field. The magnetic field modulating device switches between a state where the external magnetic field is applied to the magneto-caloric element and a state where the external magnetic field is removed from the magneto-caloric element. The state where the external magnetic field is applied may also be referred to as a magnetized state. The state where the external magnetic field is removed may also be referred to as a demagnetized state. The magnetic field modulating device modulates periodically strength of the external magnetic field which is applied to the magneto-caloric element by rotating magnetic members including the permanent magnet.